About sending mail

Does the sendmail daemon need to be running in order to send mail ?
...... I have configured a relay host on my sendmail.cf and all the mail
is being delivered successfully but I want to know what happend if I
stop the service on my AIX.

...however, if a remote server is down, then when you MUA hands a
message off to a local sendmail process over a pipe, that process may
enqueue your message locally, to be sent later by a sendmail queue
sweep.

Not sure about the AIX specifics, but on most *ix's, that means that if
you don't have a cron job scheduled to run a queue sweep, or sendmail
running with a -qmumble, that mail message may get stuck on your machine
indefinitely.

When we have systems that we want to limit SMTP accessibility, what we
do is:

1) Turn off sendmail, so it doesn't run as a daemon
2) Set up sendmail off of inetd/xinetd, tcp wrapped to only accept
connections from localhost
3) Schedule a cron job to do periodic queue sweeps

#2 is because some MUA's like to connect tcp/25 on localhost instead of
using a pipe.

For mail unix client ( mail / mailx ) sendmail daemon need not to be
running . although it takes the values from /etc/sendmail.cf files . If you
are configuring a mail server then sendmail daemon is a must.

Set your DS (smart server) in your
/etc/mail/sendmail.cf to the the Exchange server. Also
make sure your servers is in DNS and that the fully
qualified domain name is in the /etc/hosts. Use mailx
-s "Subject" -v email@removed to test.

Send the output of that if the above suggestions do
not work.

I also recompile sendmail not to listen on port 25 but
send immediately. The compiliation is the
reconfiguration of the sendmail.cf file using the m4
processor.

I know of some similar problems in customers running Active Directory and MS Exchange servers, when trying to send mail form UNIX servers it does not works ok=2E The reason is that UNIX does not authenticate with Active Directory and as a security measure, Windows Domain does not let mail from unot authenticate users=2E